1. Field of the Invention
The present invention relates mainly to an information processing apparatus such as a parallel computer system consisting of a plurality of computational nodes interconnected in a star-shaped configuration using a star coupler.
2. Related Background Art
There are two conventional methods for each computational node to use an interconnected network in a parallel computer system employing the star-shaped topology for the interconnected network: a method without performing an arbitration operation (or without providing an arbiter), in which individual computational nodes each check circumstances of use of transmission line (whether it is open or not), and a node uses the transmission line if it is open, but continues checking whether any collision is caused in the transmission line, if it is in use; or a method with an arbiter, in which a signal line for arbitration in the interconnecting network is stretched between each computational node and the arbiter, the arbiter performs arbitration to avoid any collision in the transmission line in response to requests for use of the interconnecting network from the individual computational nodes, and the computational nodes each use the transmission line, based on authorization of use from the arbiter.
Among the above conventional examples, the method without an arbiter, however, needed means for checking if the transmission line is open or not, means for detecting occurrence of collision, recovery means in detection of collision, etc., which caused a drawback that processing or apparatus became complex.
On the other hand, the method with an arbiter for arbitration had a problem in respect of the number of connecting lines between the computational nodes and the arbiter. Especially in the case of the star-shaped interconnecting network, the arbiter was normally located at the center of connecting network and therefore signal lines for arbitration and signal lines for actual data transfer were needed between the individual computational nodes and the center of connection network, which increased the number of connection lines. In order to avoid an increase in number of connection lines, there is a method employing the packet transmission method for data transfer, thereby reducing the number of signal lines (connection lines) for actual data transfer. Even with this method, double interconnections for data transfer and for arbitration were required between the respective computational nodes and the center of connection network.